1. Technical Field
The present invention relates to a drive circuit for driving a semiconductor light emitting element.
2. Related Art
There have been used image display devices irradiating spatial light modulators such as light valves or digital mirror devices (DMD) with illumination beams from light source devices, thereby displaying images. In such image display devices, laser source devices each for emitting a laser beam are sometimes used as the light source devices. Some laser source devices use a second harmonic generation element for converting an incident light into the light with a half wavelength of the incident light, thereby converting infrared light output from a semiconductor laser into the light with a half wavelength of the infrared light through the second harmonic generation element, thus obtaining visible light with high light intensity.
The laser source devices of the related art drive the semiconductor laser using a drive circuit provided, for example, with a DC/DC converter and a switching circuit. Specifically, the switching circuit controls the voltage adjusted by the DC/DC converter to form a voltage with a rectangular waveform to be supplied to the semiconductor laser, and the semiconductor laser emits light in accordance with the current flowing therethrough corresponding to the voltage thus supplied.
JP-A-2004-334083 is an example of a related art document.
The steeper the angle of the waveform representing the light intensity of the incident light is, the higher efficiency the second harmonic generation element can convert the incident light into the second harmonic wave with. However, when driving the semiconductor laser using the voltage with a rectangular waveform, a laser beam with a rectangular waveform having a peak waveform with a gentle slope is output from the semiconductor laser. Therefore, in the drive circuit of the related art, there is a problem that the conversion efficiency of the second harmonic generation element is too low to obtain the laser beam with sufficient light intensity. Further, since the drive circuit of the related art needs the DC/DC converter and the switching circuit, there is also a problem that the configuration of the circuit becomes complicated, and the light emission efficiency is low as the entire laser source device.
The problems described above are not the problems limited to the image display devices, but the problems might arise in monitor devices or lighting devices using the laser source devices.